This invention relates to a method of operating a printing press and apparatus therefor and, more particularly, to a press employing a central impression cylinder with a plurality of print decks disposed about the periphery thereof.
Illustrative of the art to which the invention applies is co-owned U.S. Pat. No. 3,041,967. There the central impression cylinder receives ink impressions (generally different colors) from six different print decks, arranged three on a side as is relatively commonplace in this phase of the printing art. Normally, each deck includes a plate cylinder arranged to impress a particular pattern on the web carried by the impression cylinder. The ink, i.e, color, is transferred to the plate cylinder which carries the plate embodying the desired pattern by means of a transfer cylinder, commonly referred to an "anilox roll". This anilox roll, in turn, derives the ink from a fountain roll operating in or in conjunction with a source of ink. Thus, there is an arrangement of three rolls in each deck for developing the pattern or "repeat" as is commonly referred to in the art. The above mentioned patent deals with a mechanism for bringing these various deck cylinders into contact so as to achieve the printing. This, however, is a relatively minor problem when compared with the problem faced by the art in changing the plate cylinders. It will be appreciated that every time the "repeat" is to be changed, the plate cylinder itself has to be changed. The major problem that arises in this transition is that of achieving register of the various colors or patterns. Often, a large, expensive machine may be inoperative for an hour or two while the pressman are adjusting the various decks to achieve registration.
The difficulty of achieving registration according to contemporary technique can be appreciated from the following typical sequence. The first step has been to install plate cylinders in all of the 6 decks. These are normally arranged three on a side with the first deck being at the 10:30 o'clock position, the second at 9 o'clock, the third at 7:30 o'clock, the fourth at 4:30 o'clock, the fifth at 3:00 o'clock and the sixth at 1:30 o'clock. The sequence of achieving register normally starts with the No. 1 deck where the pressman hits two buttons to bring the data cylinder and the anilox roll almost into gear mesh. It will be appreciated that conventionally the central impression cylinder is equipped with a large gear usually called a "bull" gear which in turn drives a gear train for the plate and transfer cylinders in each deck, these gears being arranged in tandem. Thus, the first step is to almost engage the anilox roll gear with the place cylinder gear and the plate cylinder gear with the bull gear. To achieve gear meshing, the gear on the plate cylinder is "inched" in small increments until proper mesh is achieved with the teeth on the bull gear. It also should be appreciated that these are helical gears--necessitated for fine adjustment--so that gear tooth meshing is not readily preceived visually. In the same fashion, the anilox roll gear is inched into meshing relation with the plate cylinder gear. Thereafter, the rolls of the No. 1 deck are locked in position and inched into impression position. This is normally determined by inserting a 0.125" inch gauge between the surface of the plate cylinder and the surface of the central impression cylinder--and this is required along both sides of the web, i.e., at each end of the plate cylinder. The same feeler gauge activity is performed on the ends of the anilox roll so as to bring it into proper impression position. Thereafter, a register mark is placed on either the impression cylinder or web, as desired. In some instances, both are employed because, although the register mark is much more visible on the web, it might slip relative to the impression cylinder.
The next sequence of steps involve indexing the impression cylinder until the register marks lines up with the tangent point of the No. 2 plate cylinder relative to the central impression cylinder.
Next, the plate cylinder and anilox roll of the No. 2 deck are brought into almost meshing relation and then inched into impression position utilizing the feeler gauge procedure described above. At this point, the plate cylinder is not locked to its gear so that the plate cylinder can be rotated until it is in register with the previously put down register mark, i.e., the pattern on the No. 2 deck plate cylinder is in congruence with the pattern provided by the No. 1 deck plate cylinder. Then the plate cylinder gear is locked relative to the plate cylinder. This same sequence of steps performed relative to the No. 2 print deck has to be performed with respect to the remaining print decks, i.e, decks 3 through 6 and it will be appreciated that at each stage, visual inspection of the printed pattern must be made to insure that each of the impressions provided by the six decks is in proper register. This has proved to be time-consuming and wasteful of the productive capacity of large, high speed presses. This is particularly true when short "runs" are made because the changeover from one run to another requires going through the laborious changeover procedure just described.
The obvious solution to the laborious registration procedure is to provide register marks on the central impression and plate cylinders beforehand corresponding to a given repeat. However, this has not proven successful in practice probably because of the difficulty of utilizing the large number of marks necessary to cover the spectrum of "repeats". Also, the gear teeth are relatively small and because it is difficult to discern misalignment of the order of a quarter or half degree, very often the wrong gear teeth are engaged. In this connection, it should be appreciated that the gearing is helical rather than conventional spur gears which further complicates the problem of making sure that right gear tooth is selected for engagement with the correct "valley" in mating gear so as to bring the proposed register marks into alignment. The aligned register mark expedient was suggested in Fresch Pat. No. 76 26719 but to the best of applicant's knowledge, this has not been adopted in practice. The teaching of the French patent is that the register marks on the plate cylinder and central impression cylinder should be in line after the gear teeth have been brought into engagement. This really does not address the problem because it is difficult to know which helical tooth should be selected beforehand so as to bring about the alignment after the helical teeth have meshed.